trust me these things go down very quick.
maybe a coworker or a friend will overhear a conversation or you are bragging about bitcoin and once he knows where to look it is not that hard anymore. you would be surprised how fast a friendship can end over money.
i also do not like the argument, that we can just use it for small sums. what happens is that it works for small sums and we get used to it so we start using it for big ones too.

You may be right if we are talking about trivial amounts that almost nobody would want to steal anyways. Otherwise you're naive and wrong. People are willing to do all kinds of 'bad' things for money.